The IU Cyclotron Facility is converting 50,000 sq. ft. of physics research space into a regional proton therapy center, the Midwest Proton Radiation Institute (MPRI). Clinical trials and research for development and optimization of new treatments will be conducted at MPRI. The medical director, Allan Thornton, M.D., and the technical director, John Cameron, Ph.D. are directing the conversion. The renovation will include three patient treatment rooms, a research room for radiation biology research and development of new equipment to enhance patient treatments, and a patient clinic. The first treatment room will contain a large-field fixed horizontal treatment line and an eye line. The second treatment room will be equipped with the subject of this application a 360x isocentric rotating gantry. The gantry makes it possible to rotate the beam around the patient and thus treat tumors from any angle. A gantry provides maximum efficacy in avoiding critical organs, and efficiency in patient set-up and beam delivery. This application is a request for funding to provide the gantry mechanical structure and controls, the gantry beam transport system, and the dose monitoring system for the second treatment room. The cost of the project including the first treatment room, the clinic and one gantry is estimated to be $15 million and $13 million has already been raised by Indiana University. With the addition of the $2 million being requested in this application, the gantry can be completed. If funded, the gantry installation and commissioning could be completed by June 2004.